(1) Field of the Invention
The invention relates generally to digital rights management and more particularly to securely distributing digital content.
(2) Description of the Related Art
Various content protection schemes have been devised. One example is High-bandwidth Digital Content Protection (HDCP). HDCP cryptographically manages transmission of content from a HDCP content source to a HDCP content sink. A HDCP-compliant device should contain forty 56-bit confidential cryptographic keys and use a 40-bit key selection vector (KSV) to assist with key selection. However, HDCP imposes a limit on the size of the KSV first-in-first-out (FIFO) buffer in HDCP-compliant devices. Also, some HDCP-compliant devices do not support repeaters or otherwise limit the number of KSVs supported. The inability to support repeaters can impose undesirable constraints on system topologies.
Furthermore, HDCP limits the levels of HDCP-compliant devices that may be interconnected to seven. Latency increases as the number of levels increases, and the seven-level limit allows passing KSVs from across all seven levels within a five-second time-out limit. The seven-level limit thereby also imposes constraints on system topologies.
Adding a new device downstream from a content source forces reauthentication of HDCP content sinks, which introduces an interruption of any content being provided to those HDCP content sinks. Thus, seamless reconfiguration of a system topology is not presently possible.
Layered switching causes new devices to appear, which, as described above, can force reauthentication of HDCP content sinks. Thus, switching devices can cause system-wide interruption of content just by their presence and operation in a system.
Limited interface speeds, such as limited inter-integrated-circuit (IIC) interface speeds, delay large KSV lists, which can increase latency to an extent where prescribed time-out periods area exceeded. Such increases in latency can constrain system topologies.
Switching color spaces and/or sampling requires reauthentication of HDCP content sinks, which, as noted above, causes content to be interrupted not only for HDCP content sinks that are switching color spaces and/or sampling but also for other content sinks receiving the same content.
Thus, a technique for securely and reliably distributing content over a complex system topology is needed.
The use of the same reference symbols in different drawings indicates similar or identical items.